The invention relates to a process for the production of a high frequency transistor, particularly in an integrated circuit. The transistor is in a semiconductor body and is electrically insulated from adjacent semiconductor components by insulating layers. The base zone consists of two differently doped zones of which one determines the effective emitter width and is produced by ion implantation in accordance with U.S. Patent Application Ser. No. 749,609, now U.S. Pat. No. 4,110,779 incorporated herein by reference.
In order to achieve as high as possible a degree of integration in integrated circuits, frequently high frequency transistors having a small emitter width and a small base bulk resistance are required. Usually, the minimum emitter width is determined by the lower limit values which can be attained with the photo-lacquer and etching technique. Furthermore, the base bulk resistance can be reduced by implanting a stepped profile (IEEE Transactions on Electron Devices, Vo. ED 21, No. 4, April 1974, Pages 273-278.
As is known, the oxide insulation technique has the advantage that no insulating trough with lateral insulation diffusions are required in order to electrically isolate a component from an adjacent component. Thus a higher degree of integration can be achieved with the oxide insulation technique.
In order to provide a high frequency transistor which has the least possible emitter width and a small base bulk resistance, and which exploits the advantages of the oxide insulation technique and the photolacquer and etching technique, it has already been suggested (See Ser. No. 749,609) that the base zone consists of two differently doped zones, of which the one zone establishes the effective emitter width. The zone which establishes the effective emitter width can consist of a region between an oxide layer and the other zone of the base zone.
Thus the base zone comprises a preferably p doped, active base zone and a preferably p.sup.+ highly doped, inactive base zone. The inactive base zone is bounded by the "beak-shaped" region which is formed during the oxidation of the insulating oxide layers. It is in fact in this region that the zone which is doped oppositely to the base zone runs obliquely upwards to the surface of the semiconductor body. Thus between the inactive, highly-doped base zone and the oxide layer there exists an oppositely doped region whose width represents the effective emitter width. In this way, emitter widths of 0.1 to 0.5 .mu.m can be produced independently of photo-technical processes. Furthermore, the inactive base zone reduces the base bulk resistance.
Previously, following the diffusion of the inactive base zone, the emitter window is opened and the active base zone is produced by ion implantation. This active base zone is bounded on the one side by the oxide layer and on the other side by the inactive base zone whereby a self-adjustment is provided.